Rare decay π0→e+e−\pi^0\to e^+e^-: on corrections beyond the leading order

The preceding experimental and theoretical results on the rare decay $\pi^0 \to e^+e^-$ are briefly summarized. Already computed two-loop QED corrections are reviewed and the bremsstrahlung contribution beyond the soft-photon approximation is analytically calculated. The possible further contribution of QCD loop corrections is estimated using the leading logarithm approximation. The complete result can be used to fit the value of the contact interaction coupling $\chi^r$ to the recent KTeV experiment with the result $\chi^r(M_\rho) = 4.5 \pm 1.0$.Comment: 10 pages, 9 figures, 1 tabl

Radiative corrections in Dalitz decays of π0\pi^0, η\eta and η′\eta^\prime mesons

We briefly summarize current experimental and theoretical results on the two important processes of the low-energy hadron physics involving neutral pions, the rare decay $\pi^0\to e^+e^-$ and the Dalitz decay of $\pi^0$, and provide a new value for the ratio $R={\Gamma(\pi^0\to e^+e^-\gamma(\gamma))}/{\Gamma(\pi^0\to\gamma\gamma)}=11.978(6)\times10^{-3}$, which is by two orders of magnitude more precise than the current PDG average. This value is obtained using the complete set of the next-to-leading-order radiative corrections in the QED sector, and incorporates up-to-date values of the $\pi^0$-transition-form-factor slope. The ratio $R$ translates into the branching ratios of the two main $\pi^0$ decay modes: $\mathcal{B}(\pi^0\to\gamma\gamma)=98.8131(6)\,\%$ and $\mathcal{B}(\pi^0\to e^+e^-\gamma(\gamma))=1.1836(6)\,\%$. Furthermore, we present the complete set of radiative corrections to the Dalitz decays $\eta^{(\prime)}\to\ell^+\ell^-\gamma$ beyond the soft-photon approximation, i.e. over the whole range of the Dalitz plot and with no restrictions on the energy of a radiative photon. The corrections inevitably depend on the $\eta^{(\prime)}\to\gamma^*\gamma^{(*)}$ transition form factors. For the singly-virtual transition form factor appearing e.g. in the bremsstrahlung correction, recent dispersive calculations are used. For the one-photon-irreducible contribution at the one-loop level (for the doubly-virtual form factor), we use a vector-meson-dominance-inspired model while taking into account the $\eta$-$\eta^{\prime}$ mixing.Comment: 9 pages, 3 figures; contribution to the proceedings of the following conferences: XIIIth Quark Confinement and the Hadron Spectrum, 15th International Workshop on Meson Physics and 9th International Workshop on Chiral Dynamic

Radiative modes K+→π+γ∗γ(∗)K^+\to\pi^+\gamma^*\gamma^{(*)} and the K+→π+4eK^+\to\pi^+4e decay

We discuss radiative transitions of a charged kaon to a pion and two photons. In particular, we have a closer look at radiative corrections for the $K^+\to\pi^+\ell^+\ell^-$ decays and present the branching ratio of the $K^+\to\pi^+e^+e^-e^+e^-$ process calculated for the first time at leading order in the Standard Model.Comment: 5 pages, 3 figures, 1 table; contribution to the proceedings of International Conference on Kaon Physics 2022 (KAON2022

Airborne next: rethinking airborne organization and applying new concepts

The airborne concept has had a lasting impact on military force structures since its employment on a large scale during World War II. It is puzzling to consider how little airborne organizational structures and employment concepts have changed in the intervening seven decades, considering the great amount of change occurring in warfare. This thesis examines the future potential of airborne concepts by rethinking traditional airborne organizational structures and employment concepts. Using a holistic approach in the areas of organization, doctrine, technology, and strategy as guiding frames of reference, this thesis recommends updating the organizational structures of airborne forces to model a small and many approach over a large and few approach, while incorporating a swarming concept. Utilizing historical and contemporary vignettes to demonstrate airborne utility, this research reveals how a parachute capability displays the unique attributes to complement a swarming concept. Under an updated organizational structure and new employment concept, airborne forces can offer renewed relevancy to the U.S. Department of Defense against modern adversaries in crises and conflict.http://archive.org/details/airbornenextreth1094545878Major, United States ArmyApproved for public release; distribution is unlimited

Radiative corrections for the decay Σ° → Λe+e−

Electromagnetic form factors serve to explore the intrinsic structure of nucleons and their strangeness partners. With electron scattering at low energies the electromagnetic moments and radii of nucleons can be deduced. The corresponding experiments for hyperons are limited because of the unstable nature of the hyperons. Only for one process this turns to an advantage: the decay of the neutral Sigma hyperon to a Lambda hyperon and a real or virtual photon. Due to limited phase space the effects caused by the Sigma-to-Lambda transition form factors compete with the QED radiative corrections for the decay Σ^0→Λe+e−. These QED corrections are addressed in the present work, evaluated beyond the soft-photon approximation, i.e., over the whole range of the Dalitz plot and with no restrictions on the energy of the radiative photon